Probing top-partners in Higgs + jets

TL;DR

The paper shows that while the hgg coupling in composite/Little Higgs models is blind to top-partner details at low energies due to cancellations, Higgs production with a hard jet revives sensitivity through high-virtuality loops. By analyzing Higgs+jet kinematics, particularly the high-p_T jet, the authors derive mass and coupling dependences that enable limits on top-partner parameters (M_T, sin^2(theta_R)) at the 14 TeV LHC. They develop a largely model-independent framework, map CH/LH parameters to observable mixing angles, and quantify the reach using integrated cross sections with p_T cuts, including robustness checks against PDFs and scale choices. The study suggests that with ~300 fb^-1, one can probe sin^2(theta_R) down to ~0.05 across a wide top-partner mass range, motivating more detailed NLO analyses for differential distributions to sharpen the reach.

Abstract

Fermionic top-partners arise in models such as Composite Higgs and Little Higgs. They modify Higgs properties, in particular how the Higgs couples to top quarks. Alas, there is a low-energy cancellation acting in the coupling of the Higgs boson to gluons and photons. As a result of this cancellation, no information about the spectrum and couplings of the top-partners can be obtained in gluon fusion to Higgs, just the overall new physics scale. In this paper we show that this is not the case when hard radiation is taken into account. Indeed, differential distributions in Higgs plus jets are sensitive to the top-partner mass and coupling to the Higgs. We exploit the transverse momentum distribution of the hard jet to obtain limits on the top-partners in the 14 TeV LHC run, finding that 300 ifb of data of 14 TeV LHC are sufficient to rule out top-sector mixing angles $\sin^2 (θ_R)$ > 0.05 for top-partners with masses from 300 GeV to above 2 TeV.

Figures (11)

• Figure 1: Typical diagrams contributing to $p p \to h + j$.
• Figure 2: Lines with constant mixing angle $\sin^2(\theta_R)$ in the ($f, a_T$) plane.
• Figure 3: Ratio of partonic $gg \to h +g$ matrix elements squared in a theory with a 600 GeV (top left), 1 TeV (top right) and 2 TeV (bottom) top-partner, compared to the SM value. The ratio is a function of top-mixing angle, and the $p_T$ and $y^*$ of the final state. Projecting onto $y^* = 0$ (the minimum $\sqrt{\hat{s}}$ for a given $p_T$), the ratio is a function of the mixing angle and $p_T$ alone. The matrix elements include all gluon polarizations. The dashed red line indicates where $p_{T,j} = M_T$.
• Figure 4: (Left panel) differential cross section $d\sigma/dp_T$ at a $\sqrt s = 8\, \, {\rm TeV}$ LHC for the SM (top and bottom quarks) in blue, and including a top-partner. Three different top-partner masses are shown, $600\, \, {\rm GeV}. 1\, \, {\rm TeV}$ and $2\, \, {\rm TeV}$ and two different top-mixing angles $\sin^2(\theta_R) = 0.1, 0.4$. (Right panel) same spectra, zoomed in to the high-$p_T$ range $500\, \, {\rm GeV} - 1\, \, {\rm TeV}$.
• Figure 5: (Left panel) $\delta$ as a function of $p_T^{\rm cut}$ for different values of $M_T$ and the mixing angle. (Right panel) A zoom in the interesting range of $p_T$. These plots have been generated with $\mu=\frac{1}{2} (p_T+\sqrt{p_T^2+m_h^2})$ and a $\sqrt s = 8\, \, {\rm TeV}$ LHC.